The present invention relates to a device for fitting an end of an oil pipe on a bearing structure, in particular a platform or a vessel, the end comprising a wall which is substantially cylindrical or conical in the area of the part to be fitted. In a typical but not limiting example of application, the end is formed by a stiffening sleeve comprising a sheath forming the above mentioned substantially cylindrical wall.
The stiffening sleeves or stiffeners used to limit the bending of a flexible pipe are well known, and reference may be made, for example, to the Applicant""s patents EP 0,565,445 A and FR 97 03 095.
When a flexible pipe, fitted with a stiffening sleeve and an end fitting, is winched onto a platform to be fixed there by fitting, it is necessary for the fitting device to be constructed to resist powerful stresses, comprising firstly the axial loads resulting from the weight of the submerged pipe and also, in particular, bending stresses acting on the stiffening sleeve, which stresses result in particular from the oceanic currents and the swell. It is necessary for these stresses to be appropriately absorbed in the fitting device.
The Applicant""s hitherto-known devices make use of bulky bolted assemblies, although space is a critical problem on platforms. Furthermore, the operation of connecting the assembly of pipe, device and bearing structure is made complex and time-consuming. In a particular example of a known device, the stiffening sleeve comprises a broad flange at its end which is passed through an aperture in the bearing structure, after which two thick plates are slid under the flange. The plates straddle a base solidly fixed to the bearing structure. Then the plates are bolted to the base and the flange screwed to the plates, bolts and screws being prestressed.
Moreover, document U.S. Pat. No. 5,683,205 has disclosed an intervening sleeve system making it possible to relieve stress on a pipe passing through an aperture in a floating structure by distributing the forces, in particular bending forces, over the pipe. This system is not intended either to fix a submerged pipe at one end or to bear the weight thereof.
Finally, document GB 2 317 631 has disclosed a floating system for guiding a riser, making it possible in particular to guide the riser in accordance with a vertical axis. This is therefore certainly not a device for fitting an end of an oil pipe.
The object of the invention is to propose an effective and compact fitting device.
The invention achieves its object by virtue of a device for fitting an endxe2x80x94and in particular a stiffening sleevexe2x80x94of a submerged oil pipe onto a bearing structure forming part of a platform or vessel. The end region includes a wall that is substantially cylindrical or conical in the area of the part to be fitted, and further it comprises a substantially cylindrical or conical hollow tube fixed on the bearing structure. The hollow tube has an internal diameter that is slightly greater than the outer diameter of the said cylindrical or conical wall. Two support/centering devices, a lower and an upper device respectively, are provided at the bottom and the top of the tube to interact with the wall of the pipe end region in order to support the weight of the submerged pipe and center the end or sleeve. The end is winched, in a manner known per se, until its wall is within the tube, the slightly greater dimensions of the tube and the advantageous presence of an intake funnel allow this maneuver. Because the two support/centering devices are situated some distance apart, it is possible correctly to align the end with the axis of the tube and to hold it there solidly, using the lever arm to counter the effects of the bending stress which constitutes the most critical point. As indicated, the wall of the end may be substantially cylindrical or conical, and may or may not comprise shoulders, and the tube is substantially complementary. However, it may be advantageous to allow for a little more play in the area of one of the support/centering devices; for example, in the context of a substantially cylindrical arrangement. It is nevertheless possible to arrange for the diameter of the wall to be slightly greater at the bottom, so as to reduce play there and hence reduce the size of the support/centering device while allowing easy entry of the end into the tube.
One of the support/centering devices, and preferably the upper device, is formed by at least one conical member that interacts with a shoulder provided on the end of the pipe and with a conical bearing surface provided on the said tube. The conical members may be separate members distributed circumferentially or, preferably, be formed by a two-part collar. Advantageously, the conical bearing is provided at the upper end of the said tube, and the conical collar rests there, providing both a support and a degree of centering and alignment with the axis. The shoulder provided on the end is advantageously formed by the upper edge of an annular groove formed in the cylindrical wall and partially seating the conical collar.
The other or lower one of the said support/centering devices is advantageously formed by retractable projections, distributed circumferentially (and preferably at least three in number), provided in the inner wall of the tube and capable of being forced radially inwards into contact with the cylindrical wall of the end. In a possible embodiment, each projection is formed by a pin, in one or more parts, seated radially in a radial hole in the tube, which pins are individually forced radially inwards against the tube, for example by means of a thread provided in the radial hole and on the rear part of the pin, which then forms a pressure screw. In another embodiment, each retractable projection is formed by a ball accommodated in an orifice opening radially into the tube. Advantageously, the forced radial inward movement of the ball is caused by a wedge accommodated in the wall of the said tube. The wedge may be provided at the lower end of a spike accommodated in an inner vertical passage in the wall of the hollow tube. The wedge may be formed by a ramp provided on the spike to act either upwards or downwards. Most advantageously, the movement of the spike may be actuated from the top of the device, which is more easily accessible. The movement of the spikes may be collective or individual. A hydraulic jack mechanism may be associated with each spike.
The material of the ball and that of the wedge are selected so as to limit their deformation during the thrusting of the ball out of its orifice when it acts to create a pressure on the wall of the end of the pipe. The force imparted to the wedge, and therefore to the ball, and the material of the wall of the end of the pipe at the point of contact with the balls are selected either to create a three-dimensional impression in the said wall during installation (in which case a prestress is created) or, on the other hand, to limit such an impression to a negligible depth during maximum stressing. The wall of the end may furthermore comprise, at the point of contact of the balls, a belt made from a different material from the remainder of the wall, harder or softer depending on the desired objective.
The ball-type device thus brings about centering and, in cooperation with the upper device, alignment of the end, at the same time as, by pressure and the embedding of the balls, if any, it provides a firm fixing of the end in the fitting device. Apart from its inherent advantages in terms of compactness and strength, the ball-type device according to the invention has the advantage of not requiring a redundant predetermined axial contact surface with the upper device which would necessitate very strict verification of manufacturing tolerances.